A limiter device provided in a conventional variable displacement compressor is described in JP-A-9-292003, for example. This limiter device includes a first holding member fixed to a rotary shaft of a compressor, a second holding member fixed to a pulley, and a rubber elastic member interposed in a compressed state between the first holding member and the second holding member. A driving force from the pulley is transmitted to the rotary shaft of the compressor via the elastic member during a normal operation to operate the compressor. At this time, the torque fluctuations of the compressor are absorbed by the elastic member. On the other hand, in a case where the compressor is locked because of seizure or the like, the torque of the rotary shaft exceeds a torque during the normal operation. As a result, the elastic member is deformed or broken between the first and second holding members to intercept the transmission of the driving force from the pulley to the rotary shaft of the compressor. This prevents a breakage of a driving belt connected from an engine to the pulley and protects the other auxiliary equipment associated with the engine and connected to the driving belt at the same time.
However, when a slip is caused between the driving belt and the pulley, a slip toque becomes very small in some cases, depending on the tension and the angle of contact of the driving belt connected to the pulley. This extremely reduces a design range for providing the limiter device with a connection function during the normal operation and for breaking the limiter device before causing the slip. Therefore, there are cases where it is difficult to secure the viability of the limiter device.
Further, this limiter device protects the driving belt and the other auxiliary equipment associated with the engine when a trouble such as locking or the like occurs in the compressor, but does not have a design principle of protecting the compressor itself in advance.